Test equipment for faulty electrical insulators



my m, w49., A Jv, SORENSEN 2,475,680

TEST EQUIPMENT FOR FAULTY ELECTRICAL INSLATORS Filed March 14, 1946 Wwww Wim w I@ Patented July 12, 1949 TEST EQUIPMENT FOR FAULTY ELECTRICALINSULATORS Andrew J. Sorensen, Edgewood, Pa., assignor to The UnionSwitch s Signal Company, Swissvale, Pa., a corporation of PennsylvaniaApplication March 14, 1946, Serial No. 654,355

3 Claims.

My invention relates to test equipment for faulty electrical insulators,and more particularly to equipment to detect faulty insulators used inthe supports of propulsion current conductors of electric railways.

The supports or hangers of third rails and trolley wires of electricrailways include insulation portions or insulators. For example, inmines an electric railway for hauling out the coal or ore uses a trolleywire suspended from the roof of the mine, the trolley wire beingsuspended on short hangers spaced about feet and each including aninsulator. The propulsion current circuit includes the trolley wire asone side and the bonded rails as the return side, direct current of 200to 600 volts being generally used for propulsion power. In mines, afaulty insulator of a hanger may result in the full voltage of thepropulsion current being impressed between the trolley wire and the roofand a considerable amount of current may flow from the trolley wire intothe roof and from there through various paths to the return rail system.

In coal mines, the roof consists of more or less combustible materialand in all mines there is an accumulation of dust that may becombustible. The heat developed due to the relatively heavy currentliowng at a faulty hanger can become intense enough to start a iire withattending chances of an explosion and danger to the lives of the miners.Furthermore, such a faulty hanger may result in a leakage current thatcreates a serious loss of power and such leakage current may be of amagnitude as to impair the operation of the system if there are a numberof faulty insulators,

Accordingly, a feature of my invention is the provision of novel testequipment for faulty electrical insulators.

Another feature of my invention is the provision of novel means forlocating faulty supports or hangers of the propulsion current conductorof an electric railway.

A more specic feature of my invention is the provision of improved meansto detect faulty insulation of `trolley wire hangers in coal mines.

Other features, objects and advantages of my invention will appear asthe specication progresses.

To attain the foregoing features, objects and advantagesof my invention,I provide two primary coils symmetrically spaced with the planes of bothin a commonplane. These two primary coils are preferably alike and eachis connected to an individual capacitor which is adjustable so that eachcoil and its capacitor can be tuned to resonance at a given frequency.Two secondary coils are loosely coupled one to each of said primarycoils, and the two secondary coils are connected in series `through atuning capacitor and a resistor. The secondary coils are preferablyalike and are differentially arranged in such a manner that if theprimary coils are placed symmetrically adjacent a trolley wire orconductor and a periodic or alternating current passed through suchconductor, equal and opposite volt-- ages are induced in the secondarycoils and no voltage appears across the resistor. However, if theprimary coils are disposed one on each side of a hanger, the insulatorof which is faulty, there will be a dilference between the voltagesinduced in the primary coils and in turn in the voltages induced in thesecondary coils due to the difference in the current at the two sides ofthe hanger because a portion of the alternating current ilows throughthe faulty insulator. Such difference in the induced voltages of thesecondary coils creates a corresponding voltage across the resistor. Ameter is connected across this resistor, the connection for the Ameterpreferably includinga full wave rectifier and the meter being of thedirect current type.

Thus with the equipment properly adjusted, the meter indicates zero whenthe primarycoils are placed near a trolley wire or like conductor withno insulator between them, and when placed adjacent the trolley wirewith a good insulator between them, and the meter is moved away from itszero reading when the primary coils are placed adjacent a trolley wirewith a faulty insulator between them.

A mine will ordinarily have several thousand trolleyrwire hangers and tofacilitate the testing of the hanger insulators I preferably assemblethe coils, capacitors and resistors of my equip ment in a first assemblyor unit adaptable of being carried on an auxiliary trolley pole of amine locomotive so that the unit is carried just below the trolley wireas the locomotive moves along the track. The primary coils are arrangedin this unit so that they will have a symmetrically inductiverelationship with respect to the trolley wire. Thus as the locomotivemoves along the track, the unit will pass under the hangers one afterthe other and there will be a point at each hanger at which the primarycoils of the unit are symmetrically spaced one on each side of thehanger. A source of periodic or alternating current is preferablymounted on thelocomotive and connected between the normal trolley wheeland 3 the locomotive frame to supply an alternating current to thetrolley wire.

The rectifler and meter of the equipment are assembled in a second unitthat can loe carried on the locomotive convenient for an operator ridingonrthe locomotive to read the meter, the two equipme'ilitxiitsjbeihgconnected by'silitable lead wires. With the quipm'e'nt thus mounted on alocomotive and the locomotive run slowly through the mine, each faultyhanger insulator will cause a reading of the meter thus` detect suchfaulty insulation. A relay can vloe substituted for the meter andtherelay can beused to control an indicator bell for: light, or both.Furthermore, an automatic 'marker ii lie gfoverned by the relay and eachfaulty insulator marked with white paint or tllelike.

I shall describe one form of apparatus embodying my invention cand shallthen point out the novel features thereof in claims.

In the accompanying drawings, Fig'. 1 is adi-v agraill'iiiatic view'showing one forin of 'apparatuse dying' roy/invention when' used totestthe electrical insulators :of 'a trolley 'Wire 'in 'a iir'ie. 'Fiaz isadiag'raxr'l'riiati'c vieu/showing a prefrdfmainer 'of r'r'ioilntingnvthe apparatus of Fig. 1 on a locoit e to facilitate the testing of thetrolleyiyir'e insulators. Itis understood thatniy vinvention isnot'limited to` this use aiii 'and this -one 'application'illustrat'esthe many y"places the vequipment is uls'fl. A

VIn each of trie tipo' views'likereference charac tersar'eusd todesignate siiiiilarparts. v Y Referring t'o` Fig. 1, theleffenceharacter RA desiglates the track yailS of a ihir'e trackovrryliich minelciotive's a'e perat`d,'ohly one rail heihgshownin'tli'edrawing for 'salie ofsiniplicity. The reference character TW 'designatesa trolley Wire from which 'the "electric locomotives coll-ect 'nulsion'-'nou/'enk V'rhi's trolley vWir'e TW iS 's l n spaced at sli'rtintervals. These hangers may be of d'iirer'entforrns and in tl'ieconstruction each vis secured to the' roof ofthe `n'rlne through asuitable 'fastening'ano'eacn hanger includes an insulation portion ortiri r'll' so that trie trolley wire is normanni/'insulated frorntheI'i'he ioof.

It is clear that as long as the irisul'atiir'p'ortion' of eachvlialrl-g'er HA 'is"i'ntact, lt'tle'or no current leaks from'l theltrolleyuiire'into the' roof and tnence'to the rails; out ifjtnokinsulator of a hanger' becomes v"short circuited or' (broken down, the'full "propulsion voltagel is impressed between the" trolley `vl'f'ireandthe lr'oolf 4'and a relatively largefcurrent"leaks into 'the/roof andthence to the' return' ra'ilsystem". stated here'- inbeiore, tnelieatcreated'by this leakage" current may loe' so'i'ntense as to "caus'ejaLlire, since thev roof yin coalmiiesfis'lhoreorless combustible and inVall mines 'there'is accu-mulation of dust that is' combustible; `A;eimay become the cause of' an 4explosion4` and? thereby" endanger vthelives'of the miners. n

It is also Clear thatthe'fieakag current `is"- a loss ofV power, f andyif' there aieseveral faulty in"- `sulators,. the" -resulting leakage*currentIV seri'- ously impair tlleiol)citation*4 o' the*S'Sfsteln'.l

4 According to my invention, I provide test equipment that includes apair of primary coils Pl and P2 and a pair of secondary coils SI and S2.

5 The primary coils Pl and P2 are preferably alike and are connectedacross capacitors CI and C2, respectively. These fprinary coils aresymmetrically spaced with 'the planes o'f both in a common plane, sothat the two coils when brought adjacent the trolley Wire TW havesubstantially the same inductive relationship to the trolley wire. Also,the two capacitors Cl and C2 are made adjustable so that each primarycoil and its capacitor can be readily tuned to resonance at a givenfrequency.

The secondary coils SI and S2 are preferably alike andareloosely coupledto the primary coils Pland P2, respectively, and the two secondary coilsare' disposed so that the inductive relationship `of the secondary coilSI with respect toits primary coil PI is substantially thensairie asthat of the secondarycoilSZ with respect to its primary coil P2.Secondary coils sl and sz'are included in series 'in a tuned circuitthat includes a tuning capacitor C3 and a resistor R, the secondarycoils SI and S2 being pled to oppose each other. Y

It is to be' seen tner'eforetna't wnen'prnnary cols'P] arid P2-ae'located adjacent thetr'olley wire TW and an alternating current ispassed through the trolleyWire,v 'equal voltages are induced in tlieprimary coils P] 'and P2 which calls'efsub's'tantiallly equal currents'to ovv in the two coils ty proper adjustment of the'capacitors Cl andC2. Such currents flowing' in the primary coils induce equal voltages inthe' secondary coils'Slv and'SZ owing 'to the symmetrical relatiorisnipyanuizi'entical construction of the coils. VSiricethee 'coils Si and S2are differentlally' connecteoin tn e' tunerl'circuit including capacitorC3 and resis'torR; nov voltage is ereated across resistorlafwnen'likevoltages are lnduced in the secondary coils. However, if the primarycoils 'Pl' andv P2 are placed under a hanger HA having "a` faultylinsulator so that a portion ofthe alternati-ne current 'flows throughtlle'ir'ls'llatoriiito'the roof, the' voltage induced in thee vLlri'rnarycoils P'I'I 'and P2 willl be unequal when the hanger isbetweenthe coils.vv Thi'sdifference 2in the induced voltages irl` the primarycoils vvilll create a corresponding vdifierence in the' voltagesi'ndC'dih'the Secondary coilsl Si and s2 and,tno'uilrerenceortnesecorr'olaiy coll voltages `Willcreate a "corresponding voltage acrossthe resi'st'orR. 4 I

i meter M is connected across resistR', the connection;prefealolyincliiding a full WaveL recti'l'lr Il" 'and the niet'r 'beingof the "direct current type.

Toy test trie insul of 'any on HA-,o periodic' natio ou 'asag'eneratorfzsconnectekl Wire TW and the rails throughl a t porary connection intnevicmity of the' 'orjt'ote' tested.

#are @boeterente I Q 'nectedlbet een thetrolley wireauoj the rails at aseconupoint'nottoo 'far remote from the li'ajrirgefr toller tested'. Theprimary coils PI and P2 would be first placedadjacent the' trolleyhiwirewith' no naneer lo'ettreen tlie'rna'ndfat positi H tors CI,I-C2 and"C3uiil b named' until t re issuos"K tfv th ifietf 'rte y placentadjacent "titeE trolley vli viitni theiha ger to be tested between them,and under such conditions a faulty insulator will be detected by areadin-g in the meter due to unequal current flowing in the trolley wirepast the two primary coils because a portion of the alternating currentwill flow through the faulty insulator from the trolley wire into theroof.

To facilitate testing of the thousands of hangers of a mine, I arrangethe test equipment as shown in Fig. 2. Referring to Fig. 2, a minelocomotive LO operates over the rails RA and is provided with a normaltrolley pole TP for collecting propulsion current from the trolley wireTW, such propulsion current being supplied between the trolley wire andrail by a generator not shown, and which propulsion current is generallyof the order of 200 to 600 volts direct current.

The primary coils Pl and P2, secondary coils Sl and S2, capacitors Ci,C2 and C3 and resistor R of the test equipment are assembled in a unitindicated as a whole bythe reference character TU. This unit TU isadaptable of being carried on an auxiliary trolley pole STP mounted onthe locomotive with two swivel joints 2d and 25 so that the unit TUmounted on the upper joint 25 will always ride on the trolley wire inthe same position. T'he unit TU is provided with a case or housing ofgood insulation material to protect the test equipment from the highvoltage propul sion current and preferably two wheels Hl and i5 arejournaled in the housing in a position to follow the trolley wire TW sothat the unit always has a definite position with respect to the trolleywire as the locomotive moves along the track. The several coils of theunit TU are arranged in the housing of the unit in a manner for thecoils to have a symmetrical relationship with respect to the trolleywire and with respect to each other as explained for the coils of Fig.l. The resistor R of the unit TU is connected to a meter unit MU througha cable i6.

The meter unit MU includes the rectiiier ll and meter M of the equipmentof Fig. l, and the unit MU is arranged that it can be carried on thelocomotive LO at any convenient point for an operator riding on thelocomotive to read the meter.

A source of periodic or alternating current is provided on thelocomotive LO, such source being shown conventionally at Il. This sourceof alternating or periodic current may, for example, be a small motorgenerator to generate the proper voltage of alternating current which issupplied to a primary winding l S of an output transformer, a secondarywinding I9 of which transformer has one terminal grounded to thelocomotive frame and its other terminal connected to the trolley wirethrough the usual trolley wheel, wire .at and a blocking condenser 2|. Atemporary connection 23 for the alternating current to flow from thetrolley wire to the ground may be provided and connected in the vicinityof the hangers to be tested. However, the source Il may be arranged toprovide a relatively high carrier frequency so that current ows in thetrolley wire due to the distributed capacitance and inductance of thetrolley wire to the rails and ground. ln this latter case the temporaryconnection 23 including the capacitor 22 may be omitted.

To adjust the test equipment, the unit TU would be placed adjacent thetrolley wire at a point with no hanger between the coils and the:apacitors CI, C2 and C3 adjusted in the order named to provide a zeroreading of the meter M as explained in connection with the apparatus oiFig. l.

The locomotive LO can then be run slowly over the rails to bringthe unitTU successively under each hanger. As long as the unit TU moves alongthe trolley wire between hangers and under cach hanger having a goodinsulator no reading in indicated at the meter MU, but when the unit TUpasses a hanger having a faulty insulator an indication at the meter` is.created due to the unequal voltages induced in. the coils because aportion of the alternating current flows through the faulty hangerinsulator from the trolley wire into the roof.

Test equipment such as here disclosed has the advantages that it is ofsimple and economical construction, and is of a construction that it can`be placed on `a locomotive and the insulators of the hangers of atrolley wire of a mine rapidly checked by running the locomotive overthe track.

Although I have herein shown and described but one form of testequipment for faulty electrical insulators embodying my invention, it isunderstood that various changes and modifications may be made thereinwithin the scope of the appended claims without departing from thespiritand scope of my invention.

Having thus described my invention, what 1 claim is:

1. In test equipment for electrical insulators used in trolley wirehangers of mine railways, the combination comprising, means to at timessupply an alternating current to said trolley wire, a pair of primarycoils symmetrically spaced and portable to be located adjacent saidtrolley wire with any selected one of said hangers `between them, eachsaid primary coil connected across an individual tuning capacitor tocreate a current in the coil due to the voltages induced in the coil bythe alternating current ilowing in said trolley wire, each said primarycoil and its capacitor forming a circuit tuned to resonance at thefrequency of the alternating current and which circuits are proportionedto create coil currents of substantially equal value in response to thevoltages induced in the coils when an equal value of the alternatingcurrent ilows in the trolley wires past each coil, said coil currentsbeing of diiferent values in response to voltages induced in the coilswhen more alternating current flows past one coil than the other due toa faulty insulator of the hanger between the coils, a pair of secondarycoils one coupled to each of said primary coils, said secondary coilsconnected in series through a resistor to create a voltage across theresistor proportional to the difference in the voltages induced in thesecondary coils in response to the currents created in said primarycoils, land an indicating device connected across said resistor governedby the voltage thus created across the resistor.

2. In test equipment for electrical insulators used in trolley wirehangers of mine railways, the combination comprising, means to `at timessupply an alternating current to said trolley wire, a iirst test unitincluding a pair of primary coils and a pair of secondary coils, saidtest unit adapted to be carried on a trolley pole of a locomotive of themine railway to bring the unit adjacent the trolley wire, said primarycoils spaced apart in the unit and disposed for like inductiverelationship with the trolley wire to pick up like voltages when anequal value of the @weest N 7 Y s s. '8 s 't'r'r'iatie cirr'tiiows l""7co' t primary coiis l \`1e to the voltages 'an iih'i'h`Viftg-sae-`nequa1` 'v 1 irrary coilsfiivhei'en equaijaliie vvit ria ngy currentflows in the trolley Wire st 'ach priirary coil andcoilcurrents of diff'e iS/allies :due to the voltages inced `i`i1 theprmfa'ry coil wh nore alterhating current flows in the trolley Wire pastone primary coil than 'p' "st Vtire other due to a faulty i'slator "of a*ha ger co'r'riiig between therprima'ry coils as the ntive ioves overAthe railway, said secondy coils cople'd one to each of said prifnarycoils'hndjoppositely connected in series throiigh Nafcapacitor vand aresistor to' create 'a voltage a'css`-t1ie1esi'stor in response to neqallprif i y"'co'i1 currents, and a meter unitinclud'ing an indicating dei/ice carried on the locon'iot'ive and hating-condesa@ across saidresistor 1:0 indicate such Voltage created across the resistor.

ANDREW J. SORENSEN.

sn the 'wie REFERENCES CITED "foli'lii'ring referenices are of record inthe yvirefa's Anderson D'e-c'-8, said Drir'arycils s'pacd'f'rl'ikeduc'ti @214251304 Cummings d Jn 3, 1939 tionship to thetrolley wireand each c o "2;269L584 Eldredgfe Ja'n. 13, 1942 facr s sfa iTdlalcapac'it rv ff' 4 y tr'ie'd't'o resonance at -th y FOREIGN PATENTS

